(1) Field of the Invention
The present invention relates to a technique for detecting a moving object in images based on motion information in a video including the images. The present invention relates in particular to an articulated object region detection apparatus for detecting a region of a moving object which moves changing its outline shape, such as a person, by detecting an articulated object region which is held characteristically by such a moving object.
(2) Description of the Related Art
Research and development on a region extraction technique with which a moving object is detected by extracting a region of the moving object in an image from the image including an image of the moving object (hereinafter referred simply to as “moving object”) has been widely carried out. The technique of extracting a region of a moving object is, particularly when the moving object is a person, a fundamental technique used in common for: focus control and image quality improvement processing for digital video cameras or digital still cameras; safe driving support system for vehicles; or a collision-avoidance control or a collision-avoidance alarm for a robot with people.
The technique of extracting a region of a moving object in an image includes the following two general methods: (1) a method of identifying a region of the moving object by evaluating the similarity between a moving object model prepared in advance and a candidate region in the image; and (2) a method of identifying a region of the moving object by segmenting the image into plural sub regions to calculate an amount of characteristics for each of the sub regions and integrating similar regions on the basis of the amount of characteristics.
The former method includes, as a representative method, a method of extracting a candidate of a moving object region from an image, and then evaluates the similarity between the candidate of the moving object region that has been extracted and a moving object model prepared in advance to extract a region with high similarity as the moving object region. There further is a method that utilizes a moving object model in consideration of change in shape when extracting a region of a moving object that moves changing its shape such as a walking person. According to a method described in Patent Literature 1 (Japanese Unexamined Patent Application Publication No. 8-214289), for example, a silhouette image of a moving object is extracted from plural images, as a candidate for a moving object region. Then, the similarity between a model related to a change in shape of the moving object that has been parameterized in advance and the silhouette image that has been extracted is evaluated, so that a parameter of a region with high similarity and the model are estimated. This makes it possible to apply the parameterized model also to the person that moves periodically changing shape, thereby allowing extraction of a region of the moving object.
The latter method includes, as a representative method, a method of segmenting once an image into plural sub regions, extracting an amount of characteristics based on a brightness value of a pixel in each of the sub regions, and then evaluating the similarity of the amounts of characteristics between the plural sub regions, to integrate the regions with high similarities as the same moving object region. According to the method described in Patent Literature 2 (Japanese Unexamined Patent Application Publication No. 2006-031114), for example, an image is segmented once into rectangular sub regions, the amount of characteristics is calculated based on the brightness or motion of the sub regions, and the sub regions are integrated based on an order of the similarities of the amount of characteristics, thereby allowing extraction of the region of a moving object.